This invention relates generally to methods for fabricating air bearing surfaces of sliders for magnetic disk drives and the sliders so produced.
Magnetic disk drives are used to store and retrieve data for digital electronic apparatus such as computers. In FIGS. 1A and 1B, a magnetic disk drive 1 of the prior art includes a sealed enclosure 2, a disk drive motor 3, a magnetic disk 4, supported for rotation by a spindle 5 of motor 3, an actuator 6 and an arm 7 attached to a spindle 8 of actuator 6. A suspension 9 is coupled at one end to the arm 7, and at its other end to a read/write head or slider 10. The slider 10 typically includes an inductive write element with a sensor read element As the motor 3 rotates the disk 4, as indicated by the arrow R, a layer of air proximate to the surface of the disk 4 is swept along with the disk 4. This layer of air, commonly known as windage, pushes against the slider 10 and allows the slider 10 to lift off the surface of the disk 4 and xe2x80x9cflyxe2x80x9d on an air bearing formed beneath it. Various magnetic xe2x80x9ctracksxe2x80x9d of information can be read from the magnetic disk 4 as the actuator 6 is caused to pivot in a short arc as indicated by the arrows P. The design and manufacture of magnetic disk drives 1 is well known to those skilled in the art.
FIG. 2 shows a slider 10 of the prior art. The side of the slider 10 facing up in the drawing is the side that faces the disk 4. Thus, the highest features in the drawing are those that are closest to the disk 4 when the disk drive 1 is in operation. The slider 10 has a generally rectangular shape with a leading edge 20, a trailing edge 22, a first side 24 and a second side 26. Slider 10 further includes an air bearing surface (ABS) comprising a trailing edge pad 28, a first leading pad 30 and a second leading pad 32, and in some prior art designs also includes a first side pad 34 and a second side pad 36. The slider 10 additionally includes a leading edge step 38, a trailing edge step 40, and a cavity 42. In some prior art embodiments the slider 10 also includes a first side step 44 and a second side step 46.
During manufacture, the slider 10 is etched from a single body, typically made of a two phase mixture of aluminum oxide and titanium carbide. The steps of the manufacturing process are generally illustrated in FIGS. 3A-3H and employ photolithography methods that are well known in the art. FIGS. 3A-3H show a crosssection of the slider 10 along the line 3xe2x80x943 in FIG. 2 through successive steps. In FIG. 3A a body 48 that may have a nominally curved surface is covered with a photoresist layer 50. The photoresist layer 50 is patterned and developed, and then any undeveloped material is washed away to leave a photoresist mask 52 as shown in FIG. 3B. Next, the body 48 is etched to remove material that is not protected by the photoresist mask 52. As shown in FIG. 3C, the etching creates a first surface that is recessed below the level of the initial surface by a depth H1. FIG. 3D shows the formed trailing edge pad 28 after the first photoresist mask 52 is stripped away. The steps of FIGS. 3A-3D are then repeated in FIGS. 3E-3H. A second photoresist layer 56 is formed over the body 48 as shown in FIG. 3E. The photoresist layer is formed into a second photoresist mask 58 in FIG. 3F, and the body 48 is again etched in FIG. 3G to create a second surface recessed below the initial surface by a depth H2. FIG. 3H shows the slider 10 after the second photoresist mask 58 has been stripped away to reveal the leading edge step 38 and the cavity 42.
Accordingly, as can be seen in FIG. 2, the prior art provides for two etching steps to create features at three different heights. The pads 28, 30, 32, 34, and 36 that form the ABS represent the only portions of the initial surface that remain after the two etching operations. The steps 38, 40, 44, and 46 all are recessed beneath the ABS by a depth of H1, while the cavity 42 is recessed beneath the ABS by a depth of H2.
During operation of the disk drive 1 air that is swept along with the spinning disk 4, commonly known as windage, first encounters the leading edge 20, and leading edge pads 30, 32 and leading edge step 38. As the air flow passes between the leading edge pads 30, 32 and the disk 4 a lifting force is developed that tends to drive the slider 10 away from the disk 4. Another portion of the air flow, however, passes through a gap 60 between the leading edge pads 30, 32, over the leading edge step 38, and over the cavity 42. As the air expands over cavity 42 the pressure drops and a partial vacuum is developed that tends to draw the slider 10 towards the disk 4. In stabile flight, the downward force and the upward force are in equilibrium and the slider 10 maintains a generally constant height above the disk 4, commonly known as the fly height (FH).
FIG. 4 illustrates an attitude of a slider 10 in stabile flight over a disk 4. The drawing shows how the slider 10 flies with the leading edge 20 elevated relative to the trailing edge 22 such that the plane defined by the ABS forms an angle xcex1 to the disk 4. The fly height, FH, of the slider 10 is typically defined as the distance between the trailing edge 22 and the disk 4 since the transducer is commonly located along the trailing edge 22 adjacent to the trailing pad 28. Pads 28, 34, 36 of the ABS are designed to cooperate with the leading edge pads 30, 32 to regulate, for example, the pressure drop experienced over the cavity 42. The combination of the pads 28, 30, 32, 34, 36 and the steps 38, 40, 44, 46 also influences the angle xcex1, also known as the pitch, the degree of rotation around the longitudinal line 33 known as roll, and the resistance slider 10 exhibits to changes in its flight characteristics, commonly referred to as stiffness. Stiffness with respect to fly height is especially desirable, but additionally stiffness is also desirable with respect to pitch and roll.
In prior art designs, in order to increase the pitch angle of a slider, the combined surface area of the leading edge pads 30, 32 is increased at the expense of the surface area of the cavity 42. Increasing the surface area of the leading edge pads 30, 32 creates greater lift under the leading edge 20 causing the pitch to rise. Reducing the cavity surface area, however, reduces the volume enclosed by the cavity surface and the surrounding pads and steps. It has been found that reducing this volume also reduces the stiffness of the slider in flight. Therefore, in the prior art raising the pitch angle has been found to result in a tradeoff in stiffness.
Another well known configuration for a slider 10, commonly referred to as side rail design, positions the trailing pad 28 and the transducer (not shown) close to either first side 24 or second side 26 of the slider 10. A slider 10 with a side rail design preferably will have a controlled degree of roll so that the side 24 or 26 nearest to the transducer will be closest to the disk 4.
As will be appreciated by those skilled in the art, the dimensions of the various features of slider 10 are carefully designed to control flight characteristics such as fly height, pitch, roll, and their respective stiffnesses. It will also be appreciated that the design process must also take into account factors such as the rotation rate of the disk 4 and the need to avoid the accumulation of debris on the slider 10. Modifications to the dimensions of the various features in the design process necessarily creates tradeoffs in the flight characteristics of slider 10. For example, increasing the size of the cavity 42 at the expense of the size of the leading edge pads 30, 32 will tend to cause the slider 10 to fly closer to the disk 4.
Further, during the manufacturing process, deviations in the dimensions of the various features within the established tolerance ranges will create deviations in the flight performances of individual sliders 10. Thus, deviations in the surface area of trailing edge pad 28 around some nominal value will tend to result in deviations in the fly height of slider 10. For example, a variation of 1 microinch (xcexcxe2x80x3) in the depth H1 of the leading edge step 38 and the trailing edge step 40 in a particular prior art slider 10 might result in a variation in its fly height of 0.1xcexcxe2x80x3. In the foregoing example the sensitivity of the fly height to step depth H1 would be 0.1xcexcxe2x80x3/xcexcxe2x80x3 or just 0.1. It will be readily appreciated that lower sensitivity values are desired as they indicate that sliders 10 will be more uniform one to the next in operation which can permit lower fly heights to be achieved reliably. Therefore, it is desirable to identify designs that reduce the sensitivities of the various flight characteristics to deviations within the manufacturing tolerances of the various features on the slider 10.
What is desired, therefore, is a process for manufacturing a slider that allows for greater flexibility in its design. It is further desired to create a slider with flight characteristics that are less sensitive to deviations within set manufacturing processes.
The present invention provides for an improved slider for a magnetic disk drive. The slider is provided with an air bearing surface (ABS) comprising a pair of leading edge pads and a trailing edge pad having surfaces that are substantially coplanar, a cavity that is a surface recessed below the ABS, and a plurality of steps disposed at heights intermediate between the ABS and the cavity. The steps include at least a leading edge step and a trailing edge step, each at a different depth beneath the ABS. The trailing edge step, located at a first depth, is positioned such that it is disposed between the ABS and the leading edge step, located at a second depth. The leading edge step is likewise disposed between the trailing edge step at a first depth and the cavity at a third depth. This configuration provides an advantage to a slider of the present invention over those of the prior art in that it allows the slider to fly with a larger pitch angle without sacrificing stiffness. It has been found that the pitch angle can be increased by increasing the difference between the depths of the trailing edge step and the leading edge step.
By increasing the difference in the depths between the trailing and leading edges, a slider of the present invention flies with a higher pitch angle without reducing the cavity volume and therefore without reducing the stiffness. In other embodiments of the present invention the combined surface area of the leading edge pads is reduced in order to increase the cavity volume to achieve greater stiffness. Pitch angle is not sacrificed in these embodiments because the leading edge step can be made deeper relative to the trailing edge step in order to compensate for the loss of lift created by the loss of leading edge pad surface area.
A further advantage of the present invention relates to the sensitivities of the various flight characteristics, such as fly height, to deviations in the depths within manufacturing tolerances of the leading and trailing edges. It has been found, for example, that the sensitivity of the fly height to the depth of the trailing edge step combined with the sensitivity of the fly height to the depth of the leading edge step is less than the sensitivity of the fly height to the depth H1 in sliders of the prior art in which the two steps are always at substantially the same depth. Consequently, sliders manufactured according to the present invention have a lower overall sensitivity for the fly height when all the various manufacturing tolerances are summed together.
Additional embodiments of the invention can further include side pads and side steps where the side pads also form part of the ABS and the side steps may be disposed at any intermediate height between the ABS and the cavity. The ability to alter the depths of the side steps allows their relative heights to be used as a method for adjusting flight characteristics such as roll. It will be readily appreciated that a side step closer to the disk will experience greater lift than one further away and that a slider with such an asymmetry will tend to roll in flight. In side rail sliders of the prior art, for example, a certain degree of roll is desirable in order to position the side with the transducer as close to the disk as possible. It is therefore a further advantage of the present invention that roll and other flight characteristics can be adjusted by appropriately controlling the relative depths of the side steps.
A process is also disclosed for the fabrication of a slider of the present invention. The process includes a first cycle of masking, etching, and stripping to form a first level, a second cycle to form a second level, and a third cycle to form a cavity. In the first cycle those portions of the substrate that are to be retained as the ABS are masked and the remainder of the substrate is etched to a first depth. In the second cycle those portions of the substrate that are to be retained as the ABS and those portions that are to be retained as a trailing edge step are masked and the remainder of the surface is etched to a second depth. In the third cycle those portions of the substrate that are to be retained as the ABS, the trailing edge step, and the leading edge step are masked and the remainder of the surface is etched to the depth of the cavity. This process also allows portions of the substrate to be masked and retained to form side pads and side steps in any of the three cycles. The present invention further allows for additional cycles of masking, etching, and stripping to be included so that side steps can be placed at heights other than those of the leading and trailing edge steps. The various embodiments of the process of the present invention are generally advantageous for allowing greater flexibility in the design of sliders that have improved flight characteristics, stiffnesses, and sensitivities.
These and other advantages of the present invention will become apparent to those skilled in the art upon a reading of the following descriptions of the invention and a study of the several figures of the drawings.